Remote control system



Oct. 22, 1946. v. LEWIS REMOTE CONTROL SYSTEM m Filed March 6, 1943 5 Sheets-Sheet l L. V. LEWIS REMOTE CONTROL SYSTEM Oct; 22; 1946.

Filed March 6, 1943 s Sheets-Sheet 2 INVENTOR & HI! ATTORNEY Oct. 22,1946. L. v. LEWIS REMOTE CONTROL SYS'ITEM Filed March a, 194:5 5 Sheets-Sheet 3 INVENTOR [1090 1 [ewz'r Oct. 22, 1946. v. LEWIS REMOTE CONTROL SYSTEM Filed March 6/1945 5 Sheets-Sheet 5 mv uwh M. H mm my a M QER Md m $3M W@ m R WM RMNMRQQH M L E. m M R m R Patented Oct. 22, 1946 2,409,696 REMOTE CONTROL SYSTEM Lloyd V. Lewis, Pittsburgh, Pa., assignorto The Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application March 6, 1943, Serial No. 478,252

12 Claims. (Cl. 177-353) My invention relates to remote control systems, and more particularly to centralized traflic control systems for railroads in which a central ofiice is connected with a plurality of field stations by line wires over which code signals are transmitted at times for controlling selected devices at the stations, and at other times for indicating the condition of station devices at the ofiice.

My invention is an improvement upon that disclosed in my Letters Patent of the United States No, 2,229,249, granted January 21, 1941, for Bemote control systems.

One object of my invention is the provision of a remote control system which is particularly adapted to the use of existing line Wires without interfering with their joint use for telephone or telegraph communication or for other purposes. To this end the system of my invention employs code signals of the alternating current type in which each code comprises a series of impulses of current of alternately opposite polarity and the time spacing of successive impulses determines the code character. One advantage of this type of code is that the line signals may be generated inductively and consequently no line battery is needed.

Another advantage is that signals of this type will pass readily through transformers or repeating coils, permitting line circuits to be used which are not available for battery systems. My system, however, does not require the insertion of any apparatus in series with the line, nor is a metallic connection to the line Wires essential. Furthermore, the apparatus at the oince and at the several stations is connected to the line wires in parallel and the operation of the system is independent of the relative location of the. office and the several stations, one advantage of which is that in the event of an interruption due to a break in the line service may be quickly restored by main ofiice switching, for example, by connecting the line in parallel with a spare line at its opposite ends.

A feature of my invention comprises the provision of interference preventing means which serves when two or more codes are initiated at the same time to effect their transmission sequenthe long steps of the code are registered and for a system capacity of 35 stations seven steps of the code are used. In the system herein disclosed, boththe short and long code elements are registered positively and the number of available combinations is greatly increased, six steps for example, being sufiicient for the selection of 64 stations. In respect to this feature, my invention is an improvement upon that shown in Letters Patent of the United States to Snavely et al. No. 2,183,155, issued December 12, 1939, for Remote control systems.

Another feature of my invention relates to a reduction in the number of relays required for selecting purposes. The selection of the stations is effected by the operation of a group of pilot relays, and generally requires but one such relay for each selecting step of the code. The operation of the pilot relays is so checked as to permit I their utilization in both the picked up and released positions.

Another feature of my invention comprises the provision of a pair of relays of the stick polar type arranged to remain in their last operated position when denergized, for registering the short or long character of the code elements.

. These relays are operated alternately by the code tially in a given order, and also to stop the trans- I mission of a code which is interfered with by impulses of foreign current. may then be reinitiated manually or automatically for retransmission in its entirety.

7 Another feature of my invention relates to the more efiicient utilization of the code elements.

In the system of the prior patent mentioned, only.

The interrupted code.

elements as received and serve to store their character for delivery to the proper storage relay while the next element in turn is being received.

Another object of my invention resides in provisions for allowing only one code to be stored at the control oflice at a time, thereby insuring that a series of codes set up manually in a given order will be transmitted in the same order rather than in an arbitrary order of code superiority. This arrangement is of advantage, for example, in the operation of a series of track switches to set up a route and in eifecting the clearing of a signal governing traffic movements over the route as soon as it is fully set up and eliminates the need for a route circuit network for governing the order of transmission of the codes as required heretofore. In accordance with this feature of my invention the character of the code to be transmitted is determined by the momentary operation of a selected starting button without the use of individual code determining or starting relays as generally used heretofore. The apparatus is also arranged that the latter may. be used to store a plurality of codes for transmission in a fixed order without interference when desired.

The system of my invention employs a chain of counting relays similar in number and arrangement to those Of my prior patent, but in- 3 eludes novel arrangements for governing the operation of these relays to rende them responsive only to a particular code, no other selecting relays being needed except when it is desired to have them respond to more than one code.

Another feature of my invention resides in the connection of the stick polar relays for registering code character, in series with the counting relays, whereby each counting relay together with the polar relay energized in series therewith functions like a polar-neutral relay in providing checks against improper operation. That is to say, those circuits which include polar contacts also include neutral front contacts the closing of which checks the energization of the polar relay in the normal or reverse direction and thereby indicates that its contacts are in a proper position.

Another feature of my invention resides in improved arrangements for controlling a transmitter relay for generating the code, in which each operation of the relay depends upon the closing of a different one of a series of successively prepared circuits.

Another feature of my invention relates to the provision of improved means for preventing undue delay in the transmission of codes from the different stations under conditions of heavy traffic, due to the fact that the stations normally have access to the line in a fixed order of code superiority.

IA leading object of my invention is the provision of a system of the desired scope in a form which can be readily maintained to minimize service interruptions and which is readily adaptable to widely different conditions. On the one hand, maintenance is facilitated by mounting the relays in one or more unit housings with detachable connections, while on the other hand, different conditions require a variety of units some of which may contain idle relays and may be more efficiently provided for by the use of separately mounted relays wired individually according to their location. To meet these diverse requirements those relays which are invariable, that is to say, those the functioning of which is required regardless of their location or of the scope of the installation are mounted in a detachable coding unit such as is provided in the system of my prior patent, having detachable connections to which those storage relays may be connected which vary according to the location. One improvement resides in the arrangement of the coding unit so that it may be used at the office or at any station,

only one spare unit being required for each instal lation, while other improvements comprise arrangements whereby the number of variable relays has been decreased.

A further feature of my invention resides in the arrangement of th coding unit or that certain of the steps of the code may be used to provide additional controls and indications in installations in which they are not required for station selection.

Certain features of the system of my invention disclosed but not claimed herein, are claimed in my divisional applications, Serial No. 549,276,

. filed August 12, 1944, for Transmitting apparatus for remote control systems, and Serial No. 549,- 277, filed August 12, 1944, for Selecting apparatus for remote control systems.

I shall describe one form of apparatus embodying my invention and various modifications thereof, and shall then point out its novel features in claims.

In the accompanying drawingsi Figs. 1A and 1B taken together, show in condensed form the apparatus at the control office' in a typical centralized traffic control system embodying my invention, Fig. 1A showing the office coding unit and Fig. 1B the associated oflice storage apparatus.

Figs. 2A and 2B, taken together, show the corresponding apparatus at a typical field location, Fig. 2A showing a coding unit which is structurally similar to that at the ofiice but which has different terminal connections, and Fig. 2B the storage apparatus at a station having only one unit group of devices to be controlled, each such group being identified as a station.

Fig. 2C illustrates a modification which is to be substituted for Fig. 23 at each field location where the number of devices to be controlled exceeds the capacity of a single station or panel.

Fig. 3 shows a modification of the office selecting circuits which may be substituted for a portion of Fig. 113, to provide for the storage of control codes for transmission in a given order, as hereinbefore referred to.

Fig. 4 shows a pair of relays which may be substituted for any one of the pilot relays P of the other views to obtain the requisite contact capacity when this exceeds the capacity of a single relay.

Similar reference characters refer to similar parts in each of the several views.

Referring to Fig. 1A, the reference characters Y and Z designate a pair of line wires which provide a line circuit for the centralized traflic control system of my invention. It is to be understood that these wires extend continuously the length of the territory controlled by the centralized traffic control system, and that they may be used jointly for telephone and telegraph communication like the similarly designated line wires shown in Letters Patent of the United States to Baughman et al., No. 2,803,875, issued December 1, 1942, for Remote control systems. The system of my invention utilizes the line wires to provide a channel for the transmission of low frequency alternating current of the order of six cycles per second, and communication between the ofiice and stations is effected by means of codes each comprising a series of alternations or impulses of alternately opposite polarity having a low frequency of the order mentioned, with pauses interposed to provide code character. The C. T. 0. line channel in its normal idle condition comprises the line wires Y and Z in series, with a connection bridged across the line wires through the coils l2 of a low pass filter and the high resistance winding of a line relay R at the office, as shown in Fig. 1A, and also at each station, as shown in Fig. 2A, the transmitting apparatus at the office and at each station being normally disconnected from the line. Each line relay R is of the stick polar type, like relay OR of the above-mentioned Baughman et al. patent, and is arranged to hold its contacts magnetically in their last-operated position when the line is idle and also during the pauses between successive impulses of a code, the contacts of each line relay I R normally occupying their left-hand position,

as shown.

Each coding unit, such as the one shown in Fig. 1A, includes transmitting apparatus governed by its line relay R, consisting of a starting relay ST, a master relay M, a transmitter relay T and an impulse transformer I3, this apparatus functioning as follows: Relay M is picked up,

which characterizes the code.

and is held energized to condition the'coding unit for transmission, by momentarily energizing relay ST. The closing of front contact aof relay M then completes a circuit from the supply terminal B of a suitable local source of current over back contact 01 of relay T and through the lower primary coil of transformer I3 to the common return terminal C of the local source. At the same time, the closing of front contact 01 of relay M connects the secondary winding of transformer i3 across the line wires Y and Z through the coils l2 and [2a of a low-pass filter and the closing of front contact 0 of relay M completes the first of a series of circuits governed by the associated line relay R in a manner hereinafter described, by means of which relay T is operated periodically at intervals spaced in accordance with the desired code. Each time relay T picks up, the operation of its contact d reverses the direction of the current through transformer [3. The periodic operation of relay T thus causes transformer It to deliver induced impulses of alternately opposite polarity to the line circuit, the time spacing of Each code normally comprises sixteen impulses, providing fifteen code elements of selectable character.

' Each line relay R, controls a group of slow release timing relays Ll, L2, LP and LB, corresponding to the similarly designated relays of my prior patent. The timing of these relays is governed by means of electronic rectifiers as shown, in the manner explained in the patent, the rectifiers also serving to prevent contact sparking and to minimize contact wear.

In response to the first impulse of a code, each line relay R reverses, and its right hand contact a completes a circuit from terminal B over back contact a of relay L2, back contact 0 of relay LB, through relay Ll to terminal C. Relay Ll then picks up and its contact a completes a circuit for relay L2, whereupon relay L2 picks up and completes circuits over front contacts 0 of relays L2 and L! to Dick up relays LP and LB, which relays, as will be apparent from the drawings, are arranged to pick up simultaneously and to release successively following the release of relay Li or L2. When relay L2 picks up, its contacts a and d shift the circuit for relay Ll to the left-hand contact a of relay B. so that relay Ll becomes deenergizecl, and during the remainder of the code relay Ll is energized by relay R over front contact 0 of relay LB when relay R is in its normal position, while relay L2 is'energized over its own front contact a when relay R is reversed. ,RelaysLi and L2 remain picked up during the brief intervals between successive impulses constituting the short elements of the code, and one or the other of these relays releases during each pause constituting a long element and they thus serve to indicate code character. Relay LP is deenergized upon the release of relay Ll or L2 and governs the length of the long code elements transmitted by the associated transmitter relay the system is in its normal at rest condition as,

for example, by an impulse of foreign current.

If this occurs, relays Ll, L2, LP and LB will pick up as described and then relays Ll, LP and LB will release in that order, relay L2 remaining picked up to close a local restoring circuit for relay R. extending from terminal B at front contact o of relay L2 over back contacts 0 and b of relays Li and LB and the local winding of relay R to terminal C. Relay R will thereby be restored to normal, reenergizing relays Ll, LP and LB, and then the timing relays will release in the order L2, LP, LB and LI. Each code consists of sixteen impulses and hence relay R. is operated to normal by the final impulse and the timing relays release in the order last mentioned at the end of each code. A code may be initiated only when relays LI and L2 are both released, and it follows that successive codes are spaced by an interval which is materially longer than any interval between successive impulses of a code.

Each line relay R also controls a chain of counting relays l to 8 and [6 for counting the code impulses, and in series therewith controls a pair of stick polar relays KSI and KS2 which are operated to normal or reverse to register code character in accordance with the time spacing of the impulses. When relay R reverses in response to the first impulse of a code, the energization of relay LI as above described completes a circuit from terminal B at the righthand contact 22 of relay R over front contact b of relay Ll through the upper winding of relay KSI, back contact a of relay LB, front contact 9 of relay Ll through relay l to terminal C. Relay l therefore picks up and relay KSI is held normal, as shown. Relay LB then picks up and shifts the circuit for relays KS! and I to the branch path extending from the right-hand terminal of relay KSI over front contact a of relay LB, back contact I) of relay 2 and thence over the front contact a and winding of relay I to terminal C.

If the first element of the code is short, relay KSi is left deenergized with its contacts normal as shown, when relay R is operated to the left by the second impulse, but if the first element is long, relay Ll releases before the second impulse is received and the closing of its back contact shifts the circuit for relay l to include the lower winding of relay KSI in place of its upper winding thereby reversing the direction of energizetion of relay KS! to cause the contacts of relay KS6 to move to the right. In this case relay KSi is left deenergized with its contacts reversed when relay R is operated by the second impulse. q

In response to the second impulse of a code, relay R closes a circuit fromjerminal B at its left-hand contact 22 over front contacts 6 of relay LB and b of relay L2 through relay KS2, back contact a of relay 8, front contact b of relay I through relay 2 to terminal C, whereby relay 2 is picked up and relay KS2 energized in the normal direction as shown. If relay L2 releases before the third impulse is received, relay KS2 will be reversed thereby, that is, relay KS2 is left deenergized in its normal or reverse position depending on whether the second element is short or long, while the third element is being received. Relays 3 to 8 are provided with circuits generally similar to those for relays l and 2 and are arranged to pick up one at a time in the same Way in response to the corresponding impulses of the code, each in series with relay KS! or KS2 as described.

' over contact 0 of relay 8 and the winding of relay CR to terminalC, and relay CR, picks up completing a stick circuit at its contact a whereby 7 relay CR is held energized until the end of the code. Contact I) of relay CR prepares a circuit for energizing relay l next in order after relay 8, and relays l to i operate through a second cycle in response to impulses 9 and 15 of the code. Contact e of relay CR serves to cause relay [6 to be operated in place of relay 8 in response to the sixteenth or final impulse. It will be understood that on each step except the last, relay KS! or KS2 is positioned to normal or reverse in accordance with the short or long character of the corresponding code element and is held deenergized in its last operated position to store the code character for the duration of the next succeeding code element. As explained in more detail hereinafter, contacts b of relays KS are included in circuit portions leading over Wires 5659 to coding unit terminals which may be adiustably connected externally to those terminals which lead over wires 22-21 to the right-hand terminals of the counting relay wind ings. These circuit portions provide selectively controlled connections to the common terminal C of the locaLsource which serve during the first cycle of operation of the counting relays to prevent their continued response to a code to which the apparatus is not adjusted to respond and to check the positions of the pilot relays P of Fig. 1B. During the second cycle of operation of the counting relays, the closing of contacts and d of relay CR connects wire 56 to wire 58, and wire '1 to wire 59, and thus renders the operation of the counting relays independent of the position of contacts b of KSI and KS2, and during this cycle the pole changer contacts a and c of the relays KS control the polarity of the current supplied to a series of circuits prepared by the closing of front contacts 1 and g of relay CR, completed externally by suitable connections to the coding unit terminals over wires 46-55, which as shown in Fig. 1B control the indication relays K. Relay KSI also controls relay E in accordance with the character of the first element of the code, which is made a short element in each control code transmitted from the office and a long element in each indication code transmitted from a field station. The energization of relay E conditions the coding unit to function as a receiver.

The application of the apparatus of my invention to a specific installation will now be explained, assuming for sake of illustration that it is employed in a centralized traffic control system for controlling spaced groups of traffic governing devices such as the one shown in the track plan in Fig. 2B. This group comprises a,

track switch IW and a group of signals LH and which as indicated diagrammatically on the drawings are arranged to be controlled by code by the operation of a group of polar stick relays including a switch control relay WS and the signal control relays LHS and RHS. It is to be assumed that the installation includes not more than sixteen such locations, each having a coding unit arranged as in Fig. 2A and connected by line wires Y and Z with one at the control ofilce arranged as in Fig. 1A. At the location of switch IW, the coding unit connections are arranged precisely in Fig. 2B, this location being identified as station No. 1, the connections at the other stations bein differently arranged so that each is responsive to a distinctive code call.

At the office, the coding unit connections are arranged as shown in Fig. 1B, and include a control panel for each station containing the usual complement of control levers and indication lamps, of which only the one for station No. 1 is shown, this including a starting button IPB for initiating the transmission of a control code containing the code call for station No. 1, a switch lever SW and a signal lever SIG for controlling the switch and signal relays at station No. the levers being operatively associated with the coding unit by the energization of a selector relay OIS. The indication lamps of the panel are controlled by a group of indication relays K, which are operatively associated with the coding unit by the energization of a delivery relay OID, energized in response to an indication code received from station No. 1.

Each code call comprises a distinctive combination of long and/ or short steps, four steps providing sixteen such code calls. The oflice coding unit is arranged to transmit control codes of sixteen steps or code elements, in which the first and second are short; steps three to six, comprising the code call, either short or long; and steps seven to fifteen either short or long, to selectively control nine devices at the selected station, step sixteen governing the return of the apparatus to normal at the end of the code. In the specific arrangement chosen for illustration the code call for station No. 1 comprises four long steps; the seventh step is used to control a maintainers call signal lamp MC, at the selected station, by closing a key M03, and steps eight, nine and eleven are used to control the relays WS, LI-IS and RHS in accordance with the positions of the control levers SW and SIG. The remaining steps, not needed for control purposes, are made short steps.

Each code call is set up for transmission by positioning a group of four pilot relays, P3 to P5, Fig. 1B, in a distinctive pattern, the contact d of each of these relays controlling relay T to generate a long step of corresponding number if the relay P is picked up and to generate a short step if such relay remains released.

The step by step transmission of a control code to station No. 1, in response to the operation of the starting button IPB will now be described, assuming the control levers to occupy their normal positions as shown.

The transmission of a code by any coding unit may be initiated only when the coding unit is in its normal at rest condition, so that relays LI and L2 are both deenergized. In that case terminal B at back contact 0 of relay L2 is connected over back contact d of relay Ll to wire l1, and a code may then .be initiated by connecting wires ii and I5 together to complete a circuit to pick up the starting relay ST. Assuming that button IPB is operated, under the condition described, the connection from terminal B at wire ll will be extended over contacts I) to e of button lPB to wires 13 to 16 and thence through the upper windings of each of the relays P3 to P6 to terminal C. Relays P3 to P6 pick up, as required for the code call of four long steps identifying station No. 1, and extend the connection from terminal B at wire I1 over their contacts 0 to wire [5 and thence through relay ST to terminal C. Relay ST picks up, and completes a circuit from terminal B over its front contact c, shown at the right in Fig. 1A, over back contact of relay M to wire 2| and thence over contacts e of relays P3 to P6 in series, through relay OlS to terminal C. Relay OIS picks up, and the closing of its front contact 7 connects terminal B at contact I of button IPB to wire 28 to complete a circuit over front contact a of relay 9 ST, back contacts g and h of relays LB and E through relay M to terminal C. The energization of relay M over the circuit just traced energizes the impulse transformer l3 and connects it to the line as already explained. It is to be understood that when transformer I3 is energized over the branch including back contactd of relay T the resultant line impulse is of normal polarity to operate each line relay R to the left, and when it is energized over front contact (1 of relay T the resultant impulse is of reverse polarity to operate each line relay R to the right.' The initial impulse due to the closing of contact a of relay M therefore tends to operate the relays R to the position they already occupy and is not part of the code, its purpose being to insure the proper initial magnetization of transformer l3.

When relay OI S picks up, the opening of its back contact is extinguishes any of the indication lamps of the panel, such as lamp NH, which may be lighted, thereby indicating to the operator that the code has been initiated. When relay M picks up, it completes a stick circuit for the pilot relays P extending from terminal B at front contact 6 of relay M to wire I 9, and through the lower winding and front contacta of each of the relays P3 to P6, to wire I 8, and thence to terminal C at back contact of relay E. The closing of front contact I of relay M connects terminal B directly to wire 2!, to hold relay OIS picked up, and the operated starting button IPB may now be released.

As soon as relay M picks up, relay T becomes energized over the circuit extending from terminal B at contact 0 of relay M, contact b of relay ST, through the winding of relay T and resistor 29 to terminal C, and relay T picks up to deliver the first impulse of the code to the line to reverse all line relays R in unison, each of which operates its timing relays and counting relay l as already described. In the coding unit which is transmitting the code the energization of relay LB transfers relay M to a holding circuit having one branch extending from terminal 13 over the normal contact 5 of relay R and back contact I) of relay T, and another branch extend ing from terminal 13 over the reverse contact I) of relay R and the front contact b of relay T; thence over front contacts I) and g of relays M and LB, back contact 71. of relay E and the winding of relay M to terminal C. Relay ST becomes deenergized but is made sufficiently slow release by the provision of a rectifier unitasshown so that although its energizing circuit is; opened when relayLl picks up, it remains picked up long enough to permit relay LB; to pick up to complete the stick circuit for relay M. When relay T picks up it is held energized independently of relay ST over a stick circuit including its own front contact a. When relay I picks up, a connection extends from terminal B at contact 0 of relay M over back contact I) of relay CR and front contact (1 of relay I to wire 3!. The wires 3! to 45, inclusive, provide external connections for completing a series of circuits, closed one at a time by the counting relays, for controlling the periodic operation of relay T to determine the desired. character for each. of the elements one to fifteen, respectively, of the code. Any of these wires connected to terminal B over a contact (1 or e of an odd-numbered counting relay may be connected externally to wires 6| or H to extend the connection of terminal B to the. left-hand terminal of relay T so as to shunt the relay to cause it to release. If the connection is madeto wire 6! a short odd-numbered code element will be generated for the reason that relay T will be shunted as soon as the corresponding counting relay' picks up. If the connection is made to wire ll, a long element will be generated, relay T being held energized after the counting relay has picked up until relays Li and LP release and the connection is completed by the closing of rack contact b of relay LP.

The even-numbered code elements are similarly controlled by external connections to wires Ell and Ill. The second element, for example, will be a short element when wire 32 is connected to wire 60 because a circuit will be closed to pick up relay T, at back contact (1 of relay l as soon as relay l is released following the energization of relay 2. If on the other hand wire 32 is connected to wire 70, a long element will be generated, relay T remaining deenergized until relays L2 and LP release toclose the pickup circuit at back contact c ofrelay LP.

It follows therefore that after relay T is initially picked up by the operation of relay ST it continues to operate periodically to generate a code, provided relay M remains picked up and the associated counting relays respond. Each time relay T picks up it is held energized over its stick circuit until the associated line relay R reverses to pick up an odd-numbered counting relay, contact d or e of which connects terminal B over wire 6| or H to the left-hand terminal of relay T to release it by short circuiting its winding. Each time relay T releases, relay R is operated to normal to pick up an even-numbered counting relay, whereupon the last operated oddnumbered relay releases to prepare a pick-up circuit for rela T closed over wire 60 or 10.

In the control code being described, the first step is short, due to the fact that relay T is shunted by the connection over front contact (1 of relay I and wires 31 and BI, Fig. 113, as soon as relay I picks up, the code being thereby distinguished from an indication code transmitted from a field station which, has a long first step. The second step is made afixed short step by a connection over back contact (I of relay I- and front contact (1 of relay 2, over Wires 32 and 66, over which relay T is picked up in response to the release of relay I. The front contacts d of relays P3 to P5 are nowclosed, so that wires 33 to 35 are connected to wire lllor H and the closing of thecircuits including the front contacts a! of relays 3 to 6 is delayed until relay LP releases on each of the steps three to six, thereby making these steps long. Assuming key MCB to be open, relay P! will occupy its released position, and the seventh step will be made short due to the connection from wire 3'! over back contact (I of relay Pl, to wire 6|.

The code transmission continues through the seven steps as described only if the code delivered to the line by which relays KSland KS2 are operated, is of the corresponding pattern. Unless the first step is short, the oflice relay E picks up as hereinafter described, and its back contact h opens the circuit for relay M to stop further transmission, Unless relay KS2 remains normal to register a short secondstep, relay 3 is not operated, its circuit extending from its righthand terminal over wires 22 and 56 to terminal cat the normal contact I) of relay KS2. Similarly, the operation of relay 4 is dependent upon the reversal of relay KS! to register the long third step, the circuit for relay 4 extending from wire 23 over front contact b of relay P3 to wire roma 59 and thenc to terminal C over the reverse contact b of relay KSI. Relays to I are controlled over similar circuits including front contacts b of relays P4 to P6, while relay B is controlled over a circuit including back contact b of relay Pl. It follows therefore that the office relay 8, and relay CR controlled thereby, is operated only if steps one to seven of the control code are of the desired character.

When relay CR picks up on the eighth step, its contact 22 transfers the control of relay T from the d contacts of the counting relays to a series of eight similar circuits extending from contacts e of relays 8 and l to I, respectively, to wires 38 to 45 extending over contacts b to z of relay OlS, for controlling the character of steps eight to fifteen in accordance with the positions of the levers of the selected panel in the same manner as the preceding steps are controlled by contacts d of the relays P, as above described. The circuit for step eight, for example, extends from wire 38 over contact b of relay OIS and lever SW to wire 60 or I0, and is therefore made a short step if lever SW is normal and a long step if lever SW is reversed. The signal lever SIG controls the character of steps nine and eleven, both of which are made short when lever SIG is normal as shown. Step nine is made long and step eleven short when lever SlG occupies its left-hand position, and step nine is made short and step eleven long when lever SIG occupies its right-hand position, as will be clear from the drawings. The remaining steps, in the specific arrangement described, are made short steps by the provision of direct connections from contacts d and f to i of relay OIS to wires 60 and SI.

The transmission of the code being described is terminated with the dropping of relay T to begin the sixteenth step, during which the apparatus returns to its normal at rest condition. Relay H5 is the first to release, then relays L2, LP and LB release. Relay LB releases relays M, CR and LI, and relay M releases relays P3 to P6 and OIS, and finally, relay Ll releases.

' Considering now the mannerin which the control code just described is selectively received at station No. 1, and referring to Fig. 2A, since a coding unit like that shown in this view is provided at each field location, each of which is similar to that of Fig. 1A except for its external connections, it follows that the line relays R and the timing relays at all stations operate in unison with the corresponding ofiice relays in response to the control code, likewise relays I, 2 and 3.

Each station coding unit is conditioned to function as a receiver by the energization of its relay E on the second step, as hereinafter described.

At station No. l, relays 4 to I pick up on the corresponding steps because wires 23 to 2B of Fig. 2B are connected to wire 58 or 59 and the circuits for relays 4 to l are similar to those established for the corresponding office relays when relays P3 to P6 are picked up, as already described.

It is to be understood that at each other station one or more of the wires 23 to 26 is connected to wire 56 or 51 instead of to wire 58 or 59, as illustrated in Fig. 2C, for example, and consequently at each such station the operation of the counting relays terminates before reaching the eighth step of the code containing the code call for station No. 1.

At station No. 1, however, the counting relays operate until the sixteenth step is reached, in unison with the office relays, and when relay CR picks up on the eighth step, a branch of its circuit is closed from terminal B over front contact I) of relay E to wire 9, thence through relay MCR to terminal C, over the pole changer contacts e and ,f of relay P1, whereby relay MCR is energized in the normal direction if relay P1 is released, and in the reverse direction if relay P1 is picked up.

It is to be understood that relay MCR is of a magnetic stick type and that it closes its contact to light lamp MC when energized in the reverse direction, and assumes the released position when energized in the normal direction, remaining in its last operated position when deenergized.

Assuming theeighth step of the code being received to be short, relay KS2 will occupy its normal position and the polar stick relay WS 01' Fig. 2A will be energized momentarily in the normal direction at the beginning of the ninth step over a circuit extending from terminal B at the right-hand contact I) of relay R, contact (1 of relay LB, normal contact a of relay KS2, contacts g of relays CR and E, contact f of relay I, wire 48, relay WS, wire 46 and thence to terminal C at the normal contact 0 of relay KS2. If lever SW had been reversed to make the eighth step long, relay KS2 would be reversed, and relay WS would be energized in the reverse direction on the ninth step. Relays LHS and RHS are similarly controlled in accordance with the character of steps nine and eleven, respectively, as reflected by the position of relay KSI, these relays being operated to normal or reverse on steps ten and twelve, as will be clear from the drawings.

Each station coding unit is adapted to be conditioned to transmit indication codes in response to the energization of a code storing stick relay, such as the relay ICS of Fig. 2B.

When relay I CS is energized, it connects wire l1 over its front contact I) to wire IE, to which the starting relay ST of Fig. 2A is connected,

and this relay ST when energized completes a connection from terminal B over wire 28 and its front contact a to pick up relay M. The energization of relay ICS thus corresponds to the operation of the starting button IPB in the control code already described, that is to say, it is effective When the system is at rest, to pick up relays ST and M to initiate the transmission of an indication code by relay T at station No. 1.

Relay ICS may be picked up in response to changes in the condition of any of the indicating relays at station No. 1, as hereinafter described in detail; but it is also picked up upon the delivery of a control code to station No. 1 over the circuit extending from terminal B at wire 9 through its upper winding to terminal C.

The transmission of a control code to station No. 1 will thus be followed by a transmission of an indication code from station No. 1, in which the operation of the station transmitter relay T. of the line relays R and of the timing and counting relays controlled thereby are generally similar to those already described. The indication code comprises sixteen steps in which the first is made a long step by connecting wire 3| to wire 1!, as shown in Fig. 2B, instead of to wire 6|. Wires 32 to 31, in Fig. 2B, provide connections similar to those provided for the office relay T in the control code described. Consequently steps two and seven will be short and steps three to six long, the connections of wires 33 to 36 to wire In or 13 H providing for the transmission of the code call of four long steps identifying station No. 1.

It is to be understood that at each other station one or more of the wires 33 to 36 is connected to wire 60 or 6|, as illustrated in Fig. 2C, for example, to effect the transmission of different code calls.

When the coding unit of Fig. 2A is in the transmitting condition, terminal 13 at contact e of relay M is connected to wire 19, preparing a circuit which may be completed at contact a of relay R7 through the upper winding of relay P1 to terminal C, whereby relay P1 may be controlled to make the seventh step short or long, in accordance with the position of an indicating relay RT. The circuit by which relay P1 is held energized in the receiving condition is ineffective when relay P1 is subject to control by relay R1. wire I 8 being connected to terminal 0, at back contact c of relay E.

Steps eight to fifteen of each indication code may be used to indicate the condition of eight other station devices by suitable connections to wires 38 to 45. As shown, wires 38 to 42, controlling the transmission of steps eight to twelve, are connected to contacts (2 of the indicating relays NWP, LHR, RWP, RHR and TS, while wires 43. 44 and 45 are connected to wires 60 and SI, respectively, so as to make these steps short. Since all the connections. except the one for the first step, are similar to those for the ofiice relay T already described, no further description of the detailed operations involved in transmitting an indication code is deemed necessary.

Since the first step is long, relay E at the transmitting station is not operated. This is also true of relay E at each other field station, and consequently none of these are conditioned to receive the code.

Since each transmitter has access to the line when it is free, it may happen that two or more are set into operation at the same time. If this occurs, interference is avoided by stopping the delivery of impulses to the line by any coding unit which is transmitting a code if its line relay Pt is operated by a received impulse during a pause in the operation of the associated transmitter T. If relay R is thus operated to a position out of step with the relay T it controls, the stick circuit for relay M is opened at contact b of relay R, releasing rela M to disconnect the transmitter from the line, the coding unit then being in condition to transmit its code in its entirety when the line is again free.

Since the line relays R are of the, stick polar type, relay R at a station WhiCh is transmitting a long code element is temporarily deenergized and in condition to respond to an impulse received from the line as required for the operation of this feature.

It will be readily apparent, therefore, that the use of'the line is allotted to the different stations in accordance with the relative superiority of their code calls, a short element taking precedence over a long element in each instance. Control codes transmitted from the oflice are given precedence over indication codes transmitted from the stations by the provision of a short first element in each control code and of long first element in each indication code, as already eX- be operated by the second impulse of the code delivered by the office relay T, energizing relays open and the station relay T will remain picked up until the associated relay M is released to disconnect transformer 13 at that station from the line, leaving the office transmitter in control to continue the code.

It has already been mentioned that the coding unit at each field location is arranged to receive control codes as identified by a short first element bysuitable connections for relay E. Thus in Fig. 2A, wire ll isconnected to wire [4, and since relay KS! remains in its normal position, thestation relay E is energized in multiplewith relay 2 at the beginning of the second step over a circuit extending from terminal B at the lefthand contact b of relay R, front contact e of relay LB, normal contact a of relay KSI, wires l4 and II, contact 0 of relay l and the upper winding of relay E to terminal C. Relay E therefore picks up, and completes a stick circuit over its contact a and lower winding. extending to terminal B at contact f of relay LB.

By referring again to Fig. 1A, it will be seen that the ofiice coding unit is conditioned to receive indication codes having a long first element by connecting wire H to wire 47, in which case the pick-up circuit for the oifice relay E extends to terminal B over the reverse contact a of relay KS]. As already explained, relay KS1 occupies its reverse position during the second step only if the first element of the code is long.

Referring now to Fig. 1B, it is to be understood that the key MCB controls the character of the seventh step of a control code initiated by the operation of any one of the buttons IPB to l iPB, to operate a maintainers call signal at the selected station, and the operationof this feature will now be described. Assuming that key M013 is closed, and that button lPB is operated, a control code will be initiated as already described. When relay M picks up, a circuit is closed from terminal B at its front contact 6. Fig. 1A, over wire [9 and the contact of key MCB. Fig. 13, wire l1 and the upper winding of relay P1 to terminal 0. Relay P'l therefore picks up, and its contact (I shifts the connection of wire 31 from wire 6! to wire 1!, causing relay T to generate a long seventh step during which relay Ll releases to reverse relay KSI, the control code being in other respects similar to the one already described in detail.

At station No. 1, the release of relay Ll on the seventh step completes a circuit from terminal B at contact 1 of relay LB, Fig. 2A, over back contact a of relay CR, front contact e of relay E, back contact e of relay LI, contact 0 of relay '1,

of Fig. 213, to terminal C, so that the station relay P1 picks up completing a stick circuit over its contact a and wire l8, extending to terminal B at front contact 0 of relay E.

At the oflice and at station No. 1, a circuit is prepared for relay 8 extending from wire 21 over front contact b of relay Pl. wire 59 and the reverse contact b of relay KS! to terminal C, so that relays 8 and CR pick up on the eighth step and at station N0. 1, terminal B is connected to wire 9, energizing relay MGR in the reverse direction over front contracts e and ,f of relay P1 to light lamp MC, as required. The remaining operations are similar to those occurring on the corresponding steps of the control code already described.

unit to transmit a code.

In describing the step-by-step operation of the system, it has been assumed that the apparatus of Fig. 1B has been arranged for sixteen stations, using the elements three to six of the code in different combinations of long and short elements to provide the sixteen code calls. Step two of the code is made a fixed short element by connecting wire 32 to wire Ell. A pilot relay P is provided for each of the steps three to seven, having a contact d for controlling the transmission; that is to say, each of these steps is made long or short according to the position of the associated relay P. Relays P2 to P6 maybe arranged in sixteen different ways to complete a circuit from wire 2| over their contact e to i to select any one of sixteen S relays, as indicated by the references OIS to OIBS, in Fig. 1B.

- By the addition of a pilot relay P2 to the group of relays P3 to P6, to control the character of the second step, the number of stations which the system is adapted to control is doubled, five steps providing code calls for thirty-two stations. Rela Pl, as shown, provides an additional control or indication element in each code, but this relay may be used for station selection by arranging its circuits like those for relays P3 to P6, and it follows that the system may employ codes having either five selecting steps and nine function control steps, or six selecting steps and eight function control steps, the latter arrangement providing for the control of sixty-four stations.

For the control of sixteen stations, as shown, the circuits controlled by contacts 6 to z' of the relays P consist of two sets of circuits for eight S relays each, selected over front and back contacts e of relay P3. Similarly, to control thirtytwo stations, two sets of circuits for sixteen S relays, each set like the one shown, but connected to wire 2| over front and back contacts, respectively, of a relay P2, may be used. To obtain the requisite number of contacts one or more additional relays may be provided for any of the steps. Thus for the two sets of sixteen circuits mentioned, relay P4 may be replaced by a pair of relays HA and HE, having their windings connected in parallel and their contacts a in series, as shown in Fig. 4, likewise relays P5 and P5. Any of the thirty-two circuits thus provided may be branched over front and back contacts of relay P! to provide circuits for two-S relays, as is obvious.

The pilot relays have a dual function. When the coding unit is in the receiving condition, with relay E picked up, the relays P are picked up one at a time in response to corresponding long elements of the code as received, and current is supplied to wire 2| by relay CR to pick up the selected relay S on the eighth step of the code.

Th relays P also serve to condition the coding That is to say, they may be set up in any desired combination and the corresponding S relay energized when the system is at rest by the operation of a starting button or code determining relay to initiate the transmission of a code, in which case the P relays determine the pattern of the station code call, as already mentioned.

The step-by-step operation of the apparatus of Figs. 1A and 1B in receiving an indication code will now be described. It will be assumed that the code received is one transmitted from station No. 1 as above described, in which steps one and three to six are long steps, and steps two and -seven to fifteen are short, and it will be understood that the ofiice line relay R responds to the received impulses and controls the associated timing relays, and that relays l and 2 respond as in the codes already described. Since the first step is long, relay KSI is operated to reverse in series with relay l and its right-hand contact a prepares a circuit including wires 41 and H over which relay E, Fig. 1A, picks up. On the second step, the closing of front contact e of relay E prepares pick-up circuits for the relays P which may be traced from terminal B at contact 1 of relay LB, back contact a of relay CR, front contact e of relay E, back contact e of relay Ll or L2, contacts c of relays 2 to 1 and the corresponding wires 6261, through the lower windings of relays P to terminal C. In the case of relays P2 to P6, the connection to terminal C includes wire [9 and back contact e of relay M.

Since the third step is long in the code being described, relay P3 will pick up over wire 63 and front contact 0 of relay 3 in response to the closing of back contact 6 of relay Ll on that step, and relays P4, P5 and P6 will pick up over corresponding circuits on steps four, five and six. Since the seventh step is short, relay P1 remains released.

A stick circuit is completed by each relay P which picks up in response to the closing of back contact e of relay Ll or L2, which includes its own front contact a and extends over wire l8 to terminal B at front contact 0 of relay E.

A check to insure against the failure of the relays P to assume the positions required for the code call being received is provided by the connections for the counting relays 3 to 8 which extend to terminal C over wires 22-21 and contacts b of the relays P, wires 56-59 and contact b of relay KSI or KS2. In response to each long element, relay KSI or KS2 is reversed and completes a connection to terminal C over wire 58 or 59 and front contact I) of that one of the relays P which is picked up by the same long element, to prepare a circuit for the counting relay next to be operated. If the element is short, relay KSI or KS2 remains in its normal position and the relay P is not operated, and the circuit prepared for the next counting relay includes wire 56 or 51 and a back contact b of the relay P. In case a pilot relay such as P2 is omitted, as in the case being described, the corresponding wire such as wire 22 is connected directly to wire 56 or 58, and as shown, relay 3 responds to the third impulse only if the second step is short,

.It follows that relay 8 responds to the eighth impulse of a code to pick up relay CR only when the relays P have been set up in a combination representing the code call received by the relays l to I and KS. If the first code element is long, as assumed so that relay E is picked up, relay 8 completes a circuit extending from terminal B at contact 1 of relay LB, contact 0 of relay 8,

contact b of relay E, back contacts 0 and j of relays ST and M, to wire 2|, and thence as already described in connection with Fig. 13 over front contacts e of relays P3-P6 and the winding of the selector relay OIS to terminal C. Relay OIS is thus energized in multiple with relay CR and the closing of front contact a of relay CR completes a stick circuit for holding both of these relays picked up until the end of the code. When relays OIS picks up, a branch of its circuit extending from terminal B over contact b of relay E to wire 9 is closed at contact a of relay OIS through the winding of relay OID to terminal C, whereby relay OID is energized.

The closing of contact a, of relay D then completes a circuit for operating the indication relay K1 in accordance with the character of the seventh element, this circuit having a connection to terminal B at wire 9 whereby relay Kl is energized in thenormal or reverse direction according to the position of contacts e and f of relay P7. The indication relays may be of the ordinary stick polar type, but preferably are of the type shown in Letters Patent of the United States to Agnew No. 2,301,992, granted November 1'7, 1942, for Electrical relays,.whic-h relaysare operable to their picked up and released positions by current of normal and reverse polarity, respectively, and are adapted to' remain in their last operated position when deenergized.

Contacts b to z, inclusive, of relay OiD prepare circuits for operating the relays K connected thereto in accordance with the character of steps eight to fifteen of the code. For example, the operation of relay R to the right in response to the ninth impulse connects terminal B to contact a of relay KS2, which relay is then held deenergized in its normal or reverse position to store the character of the eighth element. Relay l picks up, completing a circuit from terminal B to terminal 0 over contacts a and c of relay KS2, including contacts g of relays CR and E, contact 7 of relay l, wires 48 and 45, contact b of relay 01D and the winding of relay NWK, whereby relay NWK is energized normal or reverse to correspond with the position of relay KS2. The operation of relay R to the left in response to the tenth impulse opens the circuit for relay NWK and connects terminal B to contact a of relay KS], and also restores relay KS2 to normal and energizes relay'2, while relay KS2 is held deenergized in its normal or reverse position to store the character of the ninth element. Relay '2 completes a circuit from terminal B to terminal C overcontacts a. and c of relay KSl, including contacts 1 of relays CR and E, contact 1 of relay 2, wires 49 and 4'1, contact 0 of relay OID and the winding of relay LHK, whereby relay LHK is energized normal or reverse to correspond with the position of relay KSl.

The operations occurring during the remaining steps of the code are similar to those olescribed, as willbe readily apparent. It follows that on steps eight to thirteen, respectively, relays K'I, NWK, LHK, RWK, RHK and TK will each be operated to a position reflecting that of the corresponding indicating relay at stationNo. 1. Steps thirteen to fifteen are fixed short steps in the code being described, but additional indication relays Kl3 to Kl5 may be provided for indicating the character of these steps if required. The operation of relay R to the left in response to the sixteenth impulse picks up relay l6, and contact b of relay l6 completes the circuit for operating relay K|5 to a position in accordance with the character of the fifteenth element. Re.- lay lfi is not provided with a stick circuit and releases after a short interval. Relay R. remains in its normal position, consequently relays L2, LP and LB release in that order. Relay LB releases relays CR, E, OIS and OID, and relay E releases the energized P relays, thereby placing the apparatus in condition to receive a new code. Relay LB also deenergizes relay Ll, which is the last to release. The release of relay L'l connects terminal B to wire ll, thereby placing the apparatus in condition to initiate the transmission of a new code.

Considering now the transmitting condition of the apparatus of Fig. 1B, with reference more particularly to the upper right-hand portion of that view, which-shows circuits controlled by the buttons for controlling the relays P2 -P6 as required by various code calls. The front contacts b to e, etc. of buttons PB, which provide a connection from wires H to wire l316, correspond to the long; elements in each of the fifteen code cajlls setup by the operation of buttons IPB to IEPB. The sixteenth code call, assigned to button IBPB, does not require the energization of any of the relays P3 to P6. It follows that the code combination assigned to each of the panels may be readily identified from the drawings.

Terminal B is connected to wire I! only when the system is at rest, or at the end of a relatively long time interval following the sixteenth impulse of a code, as already explained, under which condition the operation of any of the buttons except IEPB extends the connection from terminal B to one or more of the wires 'l3-'-'l6 and thence through the upper windings of the corresponding relays P to terminal C, thereby energizing a relay P for each long element of the selected code call. The energized relays P by closing their contacts 0 complete a connection from wire I! to wire I 5 to pick up relay ST. The operation of button IBPB completes a connection from wire I! over its contact b to wire IE to pick up relay ST without operating any of the relays P, the code call for this button comprising four short steps.

When relay ST picks up, a circuit is closed from terminal B at its front contact 0 over back contact 1 of relay M to wire 2| to pick up the relay S which corresponds to the combination set up by the relays P, opening back contact it of the operated relay S to extinguish the indication lights of the selected panel. If the relays P have been positioned properly this panel will be the one containing the operated button. That is to say, relay 015 will be energized only if each of the relays P3 to P5 pick up in response to the operation of button I PB, whereupon terminal B at contact f of button IPB will be connected over contact of relays OIS to wire 28 and thence over contact a of relay ST, to pick up relay M, thereby setting relay '1 into operation to transmit the code as already described.

It is to be understood that the connection to wire 28 over contact of each of the starting buttons IPB to EfiPB includes contact 9' of the corresponding S relay. It follows that relay M will not pick up if, due to a fault, the pilot relays P do not occupy the positions required for the code call identifying the operated starting button.

When relay M picks up, its front contact 6 connects terminal B over wire [9 and the lower windings and contacts a of the energized relays P2 to P6 to wire l8 and thence to terminal C at back contact 0 of relay E, and it follows that the operated button may be released as soon as relay M picks up to initiate the code.

The condition of relays P2 to P6 cannot be dis turbed by further operation of any of the starting buttons PB because when a code is being sent or received, terminal B is disconnected from wire l7.

As previously explained, when relay M is picked up, wires 3l3'l afford connections over contacts d of the counting relays to wires 60, 6! iii and 'H for governing the operation of relay T to generate the first seven elements of the code, the character of the variable elements being determined by the positions of the contacts d of the pilot relays P in the circuits. At the beginning of the eighth step, contact b of relay CR picks up to shift the circuits for relay T to contacts e of the countin relays and wires 38-45, and thence over contacts I) to i of that one of the selector relays 01S to OIGS which is energized, and contacts of the control levers of the corresponding panel to wires (ill, 6|, I!) and H, or directly to wire 6|] or 6| when a control step is idle, and determines the character of the ninth to fifteenth elements, in the manner already pointed out.

When relay T drops in response to the energization of wire 45 to transmit the final impulse of the code, it remains released. Relay R therefore remains in its normal position, and relays l6, L2, LP, LB and LI release in that order. Relay LB releases relays M, CR and the energized selector relay S, and then relay M releases the energized relays P. Relay Ll, which is the last to release, connects terminal B to wire H to render the buttons PB efiective to control the initiation of the next code.

It is to be noted that each operation of relay '1 to generate either a short or long code element is dependent upon the closing of a circuit over one of the wires 31-31 or 38-45. A failure oi any of the circuits to close would make the element indefinitely long, allowing the timing relays to release as at the end of the code to reset the transmitting apparatus in its normal condition. A similar release at the receiving station prevents the registration of the uncompleted ele ment.

It may readily occur that an indication code will be initiated by a station at the same time that a control code for a different station is initiated. Normally the control code will take precedence by reason of its short first element, but if due to a fault, the short first element is not properly transmitted the station transmitter will retain control of the line to deliver a long first element. If this occurs, the ofiice relay E will pick up in response to the'second impulse as in the case of a normal indication code, releasing the office relay M by the opening of back contact h of relay E. Those relays P at the ofiice which were picked up to initiate the code will now release, due either to the dropping of relay M or to the reversal of polarity of the current supplied to their stick circuits over wires l8 and 19, when relay E picks up. It follows that the oifice apparatus will be conditioned at the be ginning of the second step to respond to the received code, that is, to pick up the relay P for any of the steps two to seven in accordance with the code as received.

It may also happen that two or more starting buttons are operated at the same time. The code determining contacts controlled by the starting buttons and connected to wires 72-46 are so arranged, however, that irrespective of the number of sets operated, only one set of code determining contacts is effective to determine the code and no interference occurs, due to the provision of novel circuit arrangements as will now be explained.

By reference to the drawings it will be seen that each odd-numbered button PB has a front contact e for energizing wire 15, and that wire 16 must be deenergized to set up the combination for any even-numbered button. Each of the latter has a back contact e in the connection to wire '58 which opens when the button is operated, to prevent the energization of wire 16 by operation of any higher-numbered button. Similarly, when button 3PB or APB is operated, the opening of back contact at of the operated button prevents the energization of wire E by operation of any higher numbered button. In place of back contacts in the sets of code determining contacts, back contacts of the P relays may be used with the same efifect; thus back contacts I and g of relay P3, which open in response to the operation of relay P3 by any of the buttons 5PB8PB, prevent the energization of wires M and by operation of any higher numbered button. It will be clear from the drawings that the sets of code determining contacts are connected to the conductors 13-1! in such an order that they are eiiective onlyone set at a time, in a fixed order of code superiority.

It is believed that the modification of the code determining circuits to provide code calls of five or six steps as required for the control of additional stations will be obvious from the circuits as shown. Thus, for example, to control thirtytwo stations, two groups of sixteen contact sets each may be used, each similar to the one shown except that in one group each set will have an additional contact for energizing relay P2, while the contacts of the other group will be connected over back contacts I to i of relay P2, as indicated by dotted lines in Fig. 1B.

In certain applications of the centralized traffic control system of my invention, particularly in connection with the control of train movements on single track railroads, it may be preferable to provide for the storage of codes at the control office so that when several starting buttons are operated in a rapid sequence the codes will be transmitted in order without further attention, as in the system of my prior patent. This may be accomplished by the provision of a code determining relay CS for each panel, each controlled as shown in Fig. 3.

In this modification th contacts I) to ,f of each starting button are replaced by similarly functioning contacts of the associated relay CS in the circuits of Fig. 1B, each starting button having only a single contact a. In this modification a storing relay such as OICS is picked up at once in response to the operation of the associated button IPB regardless of the condition of the coding apparatus, and is then held energized over the stick circuit extending to terminal B at back contact 111. of th associated selector relay OIS.

When wire Il becomes energized, contacts I) to f of the lowest numbered one of the operated relays CS will be eiiective to operate the P relays as required to pick up the associated selector relay S and to connect terminal B to wire 28 to initiate the code as described in connection with the circuits of Fig. 13, as will be readily apparent. In response to the operation of relays P3 to P6 by relay OlCS for example, relay OIS is picked up and its contact m inserts back contact a of relay IS in the stick circuit for relay OICS as shown in Fig. 3, whereby the circuit is opened to release relay OICS in response to the transmission of the sixteenth impulse of the corresponding control code, to allow the next energized relay CS in order to initiate the next code to be transmitted.

A contact 7 of the associated delivery relay 0 ID provides a connection to terminal B which serves to prevent the release of relay OICS by relays OIS and I6 at the end of an indicationcode, in the event that the starting button IPB is operated and relay OICS picked up, during the reception of an indication code.

' Referring now to Fig. 23, it has already been explained that this view together with Fig. 2A shows an arrangement suitable for use at a field location having a limited number of controlled devices within the capacity of a single ofilce control panel such as the one shown in Fig. 13, these devices being those required for the control of a singletrack switch IW, and a group of signals LH and RH, located atone end of a passing siding on a single track railroad, as indicated by the track plan shown. Suitable circuits for the safety control of such devices are well known, one arrangement being shown, for example, in my prior patent hereinbefore referred to, and accordingly these circuits are shown herein only in diagrammatic form, to indicate how a typical group of trafiic governing devices may be controlled by code by means of stick polar relays. Wires 46 -55 leading to the coding unit of Fig. 2A provide circuits for the control of eight stick polar control relays, of which but three are required for the simple layout shown, namely, the switch control relay WS which governs the operation of the switch machine ISM, and the signal control relays LHS and RHS which govern the signal relays Llm and RHR, to clear the signals for the desired direction of traific movement and for putting the signals manually to stop.

It has also been explained that the apparatus of Fig. 2B is arranged as required at station N o. 1 by connecting wires 22-4! to wires 56-59 in such a manner as to render the counting relays selectively responsive to the code call set up by operation of the starting button IPB of Fig. 1B. It will be apparent that the operation of the counting relays will be discontinued on one step or another of any control or indication code containing a different code call. More particularly, the station relay E responds to a short first element, indicating the oilice as the place of origin, and relay CR responds only if the second element is short and elements three to six are long, indieating station No. 1 as the intended destination, and if relay Pl corresponds in position to the character of the seventh element as received. since the station coding unit in this case responds selectively to only one code call, selector and delivery relays corresponding to relays OIS and OlD are not required, the closing of the contacts f and g of relays CR and E in the circuits including wires 46-55 bein suiiicient to indicate the selective response of the coding unit. Inother respects the circuits for controlling the stick polar relays such as WS are similar to those for the indication relays K of Fig. 13, as will be readily apparent.

Although the apparatus of Fig. 2B is arranged specifically for use at only one location, namely, at station No. 1, it will be readily apparent that similar arrangements may be provided at each other location for which nine controls or indications suii'ice, and at each such location one or more of the wires 23 to 25 will be connected to wire 56 or 57 instead of to wire 58 or 59,'the connections at each such location being arranged in a distinctive pattern to render the counting relays selectively responsive to the code call set up by the corresponding one of the starting buttons PB. Furthermore; the connections of wires 33to 36 by which relay T is controlled will be arranged at each station in a pattern corresponding to the connections for the counting relays at that station.

The initiation of indication codes by the apparatus of Fig.2B is governedby a group of three entirety.

Relay steps seven to fifteen of the code. In the specific arrangement shown, a relay R1 controls the character of the seventh element, the eighth and tenth elements are controlled in accordance with the positions of contacts d of switch indication relays NWP and RWP, and the signal relays LHR and RHR similarly control the ninth and eleventh elements. The track relay TR for the detector track section including switch IW controls the character of the twelfth element by the operation of a storing relay TS.

Relay ICH, as shown, is normally held energized over a stick circuit extending from terminal B at contact b of relay RHR over contacts b of the indicating relays mentioned, and the front contact a and winding of relay ICH to terminal C. Relay iCH is released in response to a change in position of any of these relays to extend the connection from terminal B over its back contact a. and front contact a of a relay SS through the lower winding of relay ICS to terminal C. Relay SS is a slow pick-up relay normally energized over wire I1 and consequently is released when the line is in use and becomes reenergized following the release of relay Ll at the end of a code. ICS therefore picks up in response to the closing of contact a of relay SS, after the line has been free for a time suflicient to enable relay SS to pick up, and the closing of front contact b of relay ICS connects terminal B at wire I! to wire IE to pick up relay ST. In Fig. 2A, wire 28 is connected directly to terminal B, so that relay M picks up at once to initiate the code. When relay LB picks up in response to the first code impulse, a circuit is closed from terminal B at front contact f of relay LB over back contact a of relay CR to wire l0 and thence over contact 0 of relay lCS through relay I CH to terminal 0, whereby relay ICI-I is picked up to reestablish its stick circuit. Relay ICS is held energized until the final step of the indication code is transmitted, over a stick circuit'including its contact a and wire 20, extending to terminal B at back contact a of relay l6, and thus maintains the coding unit in condition to initiate an indication code repeatedly, if necessary, until such code is transmitted in its Relay CR disconnects terminal B from wire ID on the eighth step, consequently a change in the position of any of the indicating relays occurring after relay CR picks up is eifective to release relay ICE to effect the transmission of a second code.

An indication code follows each control code received by the station, even though the control code causes no change in the position of any of the indicating relays, for the reason that during each contro1 code received, the delivery wire 9 is connected to terminal B as already explained, and as will be clear from Fig. 2B, relay ICS is thereby energized over its upper winding to establish the stick circuit including its lower winding. At the end of a control code, wire 9 remains connected to terminal B until after relay It to reestablish the connection to terminal B at releases wire 20, consequently relay ICS remains picked p.

Relay TS provides means for insuring the transmission of an indication of the occupancy of the track section controlling relay TR, even though the section is vacated before the indication is transmitted. Relay TS picks up in response to the release of relay TR and if relay TR then picks up again, relay TS is held energized over a stick circuit including back contact b of relay [CI-I until relay ICS picks up, and then over front contact d of relay lCH, releasing after the transmission of the corresponding track occupied code, provided relay TR is then energized. When relay ITS releases, its contact b operates to release relay iCH to effect the transmission of a "track clear code.

In installations having a large number of stations and controlling heavy trailic it may happen that the number of changes occurring is sufficient to keep the apparatus in continuous operation for considerable periods of time, resulting in undue delay in the delivery of codes from inferior stations if the stations are given access to the line in a given order of code superiority as described.

Relay SS provides means for preventing undue delay under this condition. Assuming for example, that several stations initiate codes at the same time, it will be evident that the codes will be transmitted in a fixed order each relay CS which picks up at the beginning of the series of codes being released at the end of its code, until all are released. When wire I! becomes energized at the end of each code, a relay ST will be picked up to initiate the next code before relay SS has had time to close its contact a. Consequently no additional relays CS can be picked up. In other words, each station unit is allowed to transmit only one code if some other station has a code stored for transmission, for the reason that its relay CS cannot be picked up in response to a change in station conditions unless the line has been free for an interva1 somewhat longer than the normal interval between successive codes.

Referring now to Fig. 20, this view together with Fig. 2A shows the apparatus required at a field location at which the number of controlled devices exceeds the capacity of a single ofiice panel, as for example, would be the case in the control of a remotely controlled interlocking as indicated by the track plan in Fig. 11 or my prior patent. In Fig. 20 as shown, it is assumed that the location includes four groups of devices each similar to that of Fig. 2B, comprising stations Nos. to 8, inclusive, of which only station No. 5 is shown.

The code combination required for each of the different stations may be readily ascertained from the connections of the starting button contacts as shown in Fig. 1B. In View of the description of that view and of Fig. 23 already given, it will be readily apparent that the apparatus of Fig. 2C is connected to respond to the code calls set up by the operation of buttons 5P to 8P, in which step three is long and step four short. These code calls differ one from another only in respect to steps five and six, and the two relays P5'and P6 provide circuits for the selection of four relays 58 to 88 similar to the correspondingly numbered selector relays 05S to 08$ of Fig. 1B.

With the apparatus of Fig. 2C in the receiving condition it is clear that any one of the four codes to which it is adapted to respond will sufiice for the operation of the maintainers call signal MC, accordingly this feature is arranged as in Fig, 23. I

The circuits for operating the stick polar relays such as relay 5W8 difier from those of Fig 2B in that they are selected over contacts of the associated delivery relay 5D, and they are consequently similar'to those for the indication relays K of Fig 1B, already described.

The step-by-step operation of the apparatus of Figs. 2A and 20 in response to a control code transmitted to station No. 5, for example, will now be described.

Assuming the system to be in its normal at rest condition, the operation of the office starting button 5PB picks up relays P2, P4 and P5 of Fig. 1B, energizing relay ST of Fig, 1A to pick up relay 05S, thereby connecting terminal B to wire 28 to pick up relay M of the office coding unit to initiate the code, which differs from the one already described in detail, by having a short fourth step. It is to be understood that the coding unit for stations 5 to 8 is the only one responsive to codes having a long third step and a short fourth step and consequently the only one at which relay 5 picks up. Relay E, Fig. 2A picks up in response to the short first step and prepares a circuit closed when relay Ll releases on the long fourth step, over wire 65, to pick up relay P5, Fig. 2C, Relay Ll reverses relay KS1, and the closing of front contact I) of relay P5 connects wire 25 to wire 59 extendin to terminal C at the reverse contact I) of relay KSI so that relay 6 of the station coding unit picks up in'unison with the office relay 6, which is energized over a similar circuit. In a similar manner, relay P6 of Fig, 2C is picked up on the sixth step to prepare a circuit for relay 1. At the ofiice and at the location of stations Nos. 5 to 8, relay I picks up on step seven, and then on step eight, relays 8 and CR pick up, and at the field location terminal B is connected to wires 21 and 9 to pick up relays 5S and 5D, in turn, and to operate relay MCR in accordance with the character of step seven. The closing of contact a of relay 5D completes a circuit from terminal B through the lower winding of relay 50S to terminal C, so that relay 50S picks up. The closing of contacts I), c and e of relay 5D connects relays 5WS, 5LHS and 5RHS to the wires 48, 49 and 5| leading to the coding unit to prepar circuits for operating these relays in accordance with the character of steps eight, nine and eleven, re- 50 spectively, as already described. When the sixteenth step is reached, the apparatus restores to normal in the usual manner, but relay 5CH remains picked up over a stick circuit extending from terminal B at back contact is of relay 58 over its own front contact a and lower winding to terminal C.

If button 8 PB had been operated in place of button 5PB, for example, steps five and six of the code would have been short steps and relays P5 and P6 would have remained released, resulting in the operation of a selector relay 8S and the corresponding delivery relay 8D, not shown, to deliver the code to station No. 8. If, however, due to a fault, relay P5 or P6 at the station fails to pick up on the corresponding long steps of a code for station No. 5, relay 8S is not operated for the reason that in that case the station counting relay 6 or I will not be operated.

The transmission of indication codes by the apparatus of Fig. 2C is effected by the provision of a pair of relays such as the relays 50H and 50$ for each group of devices, together with a single relay SS, which relays function like the corresponding relays of Fig. 2B. In Fig. 20 each relay CS is provided with addi- 25 tional contacts for operating the station pilot relays P over circuits similar to those controlled by the starting buttons PB in Fig. 1B, in other words, they function as described in connection with relay OICS of Fig. 3, except that the check circuit including wire 28 is omitted. It follows that if relay 503 is picked up, the release of relay Ll at the end of the control code described completes a circuit from terminal B at wire I! over contacts 02 and 'e of relay 5C8, wires and 16 through relays P5 and P6 to terminal 0 so that relays P5 and P6 pick up, extending the connection of terminal B over their contacts 0 to wire l5 to pick up the station starting relay ST, which inturn picks up relays 5S and M to initiate an indication code in which steps one, five and siX are long and 7 steps two and four are short, to select the otlic'e panel for station No. 5, and in which steps seven to fifteen are controlled by a group of indicating relays selected by relay 58. It will be clear that in Fig. 2C, the connections from wire I! to wires 75 and H3 are so arranged that if the relays 508 to 8C5 are all energized at the same time, the corresponding codes will betransmitted one at a time in order without interference. Relay SS in Fig. 2C controls the connection to terminal 0 for the upper winding of each of the relays 5C8 to BCS, and functions as described in connection with Fig. 23, so that codes for indicating changes occurring after the relays CS have been picked up will be stored by the relays CH and the correspending relays CS cannot be reenergized until each of the relays CH energized at the beginning of the series has transmitted its code.

In the event the office and one or more stations initiate codes at the same time, the transmission of the second impulse by the ofiic'e transmitter to make the first step short will open the stick circuit for each field station relay M, if closed, and will also pick up relay E at each field location, and at each location such as that of Fig. 2C at which one or more relays P have been picked up, these relays will be released due to the reversal of the polarity of the current supplied to their stick circuits as already explained in connection with the similar relays of Fig. 13. Consequently only the oflice transmitter remains in operation and the apparatus at each station is in proper con-- dition to respond to a control code containing the corresponding station code call. In Fig. 20, the release of the P relays prepares a circuit for a selecting relay 8S similar to relay 58 shown, but this relay will not be operated unless the corresponding code call is received so as to enable the counting relays to respond to the first eight impulses of the code.

In view of the similarity of Fig. 2C to Fig. 1B,

it will be readily apparent that additional relays -P controlled over one or more of the steps two to seven of the code may be provided to expand the capacity to eight, sixteen, thirty-two, or sixtyfour stations, at the same field location, and that any of the code calls not used at a given location may be used at other locations.

Although. I have herein shown and described only one form of remote control apparatus en bodying my invention and several modifications thereof, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departingfrom the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1, In aremote control system, an oifice and one or more stations connected by a normally deenergized communication circuit comprising two normal or reverse position when deenergized and havin a winding connected across the line wires, one such relay being located at the office and one at each station, a plurality of code transmitters including one at the oflice and one at each station each effective when initiated to deliver to the line wires a code ofimpulses of alternately opposits polarity characterized by the relative lengths of the time intervals between successive impulses, each impulse acting to operate said line relays in unison to normal or reverse, code responsive means controlled by each line relay in accordance with the character of said codes, and means controlled locally by each line relay for restoring such relay to its normal position in the event the relay remains reversed for a predetermined time interval which is longer than any of the time intervals insaid code.

2. In a remote control system, an mice and one or more stations connected by a normally deenergized communication circuit comprising two line wires, a plurality of line relays of the stick polar type each arranged to be held locally in its normal or reverse position when deenergized and having a winding connected across the line wires, one such relay being located at the ofiice and one at each station, a plurality of code transmitters including one at the crime and one at each station each including an impulse transformer normally disconnected from theline wires, and a master relay, means controlled by each master relay when energized for connecting the associated impulse transformer across the line wires and for periodically energizing said transformer to deliver to the line wires a code of impulses of alter= nately opposite polarity characterized by the time spacing of successive impulses, each impulse act'- ing to operate the line relays in unison to normal or reverse, code responsive means controlled by each line relay in accordance with the time spacing of said impulses, and means controlled by each line relay acting to automatically restore the relay to its normal position if it is operated to its reverse position by an impulse which is not followed by other impulses to constitute a code.

3. In a remote control system, an oifice and one or more stations connected by a normally deenergized communication circuit comprising two line Wires, a plurality of line relays of the stick polar type each arranged to he held locally in its normal or reverse position when deenergized and having a winding connected across said line Wires, one such relay being located at the office and one at each station; a plurality of code transmitters including one at the office and one at each station each effective when initiated to deliver to the line Wires a series of inductively generated impulses of alternately opposite polarity each impulse acting to operate the line relays in unison to normal or reverse, said codes being characterized by pausesgfollowing certain of the impulses during which the line relays are held locally in their last operated positions, code responsive means controlled by each line relay in accordance with the character of said codes, and means controlled by each relay acting to automatically restore the relay to its normal position if it isoperated to a reverse position by an impulse which is not followed by other impulses to constitute a code.

4'. In a remote control system, an oifice and a station connected by two line wires, ,aline; re-

27 lay of the stick polar type connected across said line wires at the ofiice and also at said station, a code transmitter at the oiiice and at the station each effective when initiated to deliver to the line wires a series of inductively generated impulses of alternately opposite polarity to operate the line relays, said codes being characterized by pauses following certain of the impulses during which the line relays are held locally in their last operated positions, and means for discontinuing the delivery of impulses by each code transmitter during any pause in its operation when transmitting a code if the associated line relay is operated during said pause by an impulse received from said line wires.

5. In a remote control system, an office and a station connected by a normally deenergized communication circuit comprising two line wires, a line relay of the stick polar type at the office and at said station each arranged to be held locally in its normal or reverse position when deenergized and having a winding deriving its energization from impulses delivered at times to said line wires, a code transmitter at the office for delivering impulses to said line wires to momentarilyenergize said line relays, means at the ofice for actuating said code transmitter periodically to deliver to the line wires a series of impulses of alternately opposite polarity, stepping means controlled by the oifice line relay for counting the impulses and for controlling said code transmitter, thereby interposing pauses following certain of the impulses during which the line relays are held locally in their last operated positions, code responsive means comprising stepping means controlled by the station line relay to count the impulses, and means selected by said stepping means which is selectively controlled in accordance with the time spacing of the impulses.

6. In a remote control system, a plurality of stations connected by a normally deenergized communication circuit comprising two line wires, an impulse transformer normally disconnected from the line wires effective when operated to reverse and normal positions to supply impulses of reverse and normal polarity to the associated impulse transformer, located at each station, a stick relay at each station effective when energized to connect the associated impulse transformer to the line wires and to operate the associated transmitter relay repeatedly to reverse and normal positions to deliver a code of impulses of alternately opposite polarity through such impulse transformer to the line wires, each such code being characterized by pauses following certain of the impulses, a line relay at each station of the stick polar type operable to reverse and normal positions in response to such impulses, means for holding each line relay locally in its last operated normal or reverse position during said pauses, starting means for each stick relay effective only when said communication circuit is in its normally deenergized condition for picking up such stick relay to set the associated transmitter relay into operation to deliver its code, and lockout means effective in the event a plurality of said transmitter relays are set into operation at the same time to discontinue the operation of all but one, comprising a holding circuit for each stick relay including its own front contact and contacts of the associated line and transmitter relays by which one stick relay is held energized for the duration of its code, and each other stick relay is released to terminate the delivery of impulses by the associated transmitter in the event the 28 line relay associated therewith is operated by an impulse delivered by another transmitter during a pause in the operation of said associated transmitter.

'7. In a remote control system, a plurality of stations connected by two line wires, a two position polarized line relay having access to said line wires at each station, a code transmitter at each station having a contact operable to normal and reverse positions to deliver codes of impulses of alternately opposite polarity to said line wires to operate the line relays to normal and reverse positions, the codes being characterized by pauses between selected impulses during which the line relays are deenergized, means associated with each line relay for maintaining it in the position to which it is operated by each impulse, until the next impulse is received, and interference preventing means controlled by each line relay and by the associated transmitter relay comprising a circuit which is closed either over their normal contacts or over their reverse contacts as long as the line relay responds to the code operation of such transmitter relay but which is opened when the line relay is operated by an impulse received during a pause in the operation of the associated transmitter relay, the opening of said circuit being effective to discontinue the operation of said transmitter relay.

8. In a remote control system, two coding units each including a receiver selectively responsive to multiple element codes including selecting elements and a transmitter controlled by the associated receiver for transmitting such codes, a plurality of pilot relays in each coding unit including one for each selecting element of a code, a plurality of selecting relays in each coding unit including one for each different combination of said selecting elements in a code, energizing circuits for said selector relays including contacts of said pilot relays, there being one such circuit for each different arrangement of said pilot relays in their operated or released positions, a first relay in each coding unit selectively responsive to a first element in a code provided such element is of a particular character identifying the code as one transmitted by the other coding unit, means rendered effective when said first relay is energized for energizing each pilot relay of the associated coding unit or not depending upon the character of the corresponding selecting element being received, and for then energizing that selector relay the circuit for which includes a closed contact of each pilot relay, means in each coding unit effective only when such coding unit is in a normal at rest condition for operating the pilot relays as required to prepare the circuit for a particular selector relay of such unit and for then energizing such selector relay, and means controlled by the operated selector relay for setting the associated transmitter into operation to transmit a code having a first element to which said first relay of the other coding unit is responsive, and selecting elements of which the character is determined by the positions of said pilot relays to thereby energize the corresponding pilot relays and selector relay of the other coding unit.

9. In a remote control system, an office and a plurality of stations connected by a normally deenergized communication circuit comprising two line wires, a code transmitter at the office and at each station, each comprising an impulse transformer normally disconnected from the line Wires and a transmitter relay effective when operated to reverse and normal positions to supply impulses of normal and reverse polarity thereto, a plurality of stick relays including one at the ofiice and one at each station each serving as a master relay which when energized connects the associated impulse transformer to the line wires and operates the associated transmitter relay repeatedly to reverse and normal positions to deliver a code of impulses of alternately opposite polarity through'the transformer to the line wires, each such code being characterized by pauses following certain of the impulses, a plurality of line relays of the stick polar type including one at the oilice and one at each station, each responsive to the codes supplied to said communication circuit, means associated with each such relay for restoring it to its normal position when said communication circuit is in its normal deenergized condition and for holding it in its last operated position during each pause in a code, a pick-up circuit for each master relay including contacts closed only when no code is being delivered to said communication circuit, and a stick circuit for each master relay which includes its own front contact and which has two branches one of which is closed only when the associated transmitter and line relays are both in their normal positions and the other only when these relays are both in their reverse positions, so arranged that each master relay is held energized for the duration of the code delivered by the associated transmitter but only if the associated line relay is not operated by an impulse delivered by another transmitter during a pause in such code.

10. In a remote control system, a coding unit for controlling selected devices at the same or at a distant location by distinctive codes, each of which includes a group of selecting elements and an additional element, each of one character or another, the selecting elements being arranged in diiferent patterns to select diiferent devices, said coding unit comprising a series of pilot relays including one for each selecting element, a plurality of selector relays including one for each controlled device, a master relay, and code receiving and transmitting means; means responsive to the operation of said receiving means when said transmitting means is idle for selectively energizing said pilot relays only one at a time each in response to a corresponding element of said one character in the received code, stick circuits controlled by the receiving means for holding each energized pilot relay picked up until the end of such code, a circuit including contacts of all of the pilot relays closed after the last selecting element is received for energizing the selector relay for the code pattern indicated by the positions of said pilot relays, means controlled by said selector relay for controlling the corresponding device in accordance with the character of the additional element in such code, a plurality of locally controlled contact sets including one for each difierent code pattern each effective if operated when said receiving means is idle to selectively energize said pilot relays as required to form the corresponding code pattern and to complete circuits for the selector relay for such code pattern and for said master relay, means controlled by said master relay when energized for initiating the operation of said transmitting means to deliver a code to the line circuit to which said receiving means is responsive, circuits controlled by said master relay for maintaining the energized pilot relays and said selector relay picked up until the end of such code, and means controlled by said receiving means for governing the character of the selecting elements in the transmitted code in accordance with the positions of said pilot relays and for governing the character of said additional element in accordance with the position of a movable device selected by the energized selector relay.

11. In a remote control system, a coding unit for transmitting and receiving codes each of which includes a group of selecting elements arranged in different patterns in different codes, a group of pilot relays in said unit including one for each selecting element, which assume energized or released positions in distinctive combinations to register the code patterns, two circuits for energizing each pilot relay, means effective when a code is being received by said coding unit for completing one circuit for each pilot relay the energization of which is required to register the code pattern being received, such relays being thereby energized one at a time as the selecting elements are received, starting means for each different code for initiating the transmission of a code by said coding unit, each effective if operated when no code is being received by said unit to complete the other circuit for each pilot relay the energization of which is required to set up the code pattern identifying the operated starting means, and means for controlling the character of each selecting element in the transmitted code in accordance with the position of the correspondin pilot relay.

12. In a remote control system, a coding unit for transmitting and receiving codes each of which includes a first element of distinctive character and a group of selecting elements arranged in different patterns in different codes, a group of pilot relays in said unit, including one for each selecting element, which assume energized 'or released positions in distinctive combinations to register the code patterns, starting means for selecting the diiferent code patterns for transmission each including means for energizing each pilot relay by current of a given polarity if the energization of such I relay is required for the corresponding code pattern, said starting means being effective only when said coding unit is in a normal inactive condition, means for energizing said pilot relays one at a time by current of the opposite polarity each in response to a different selecting element of a given character in a received code to register the code pattern of such code, a stick circuit for each pilot relay closed when such relay is picked up and supplied with current of the proper polarity to maintain such relay picked up until the end of the corresponding code, and means controlled by the first element of a code received when one or more of said pilot relays have been picked up to transmit a code having a given pattern, for reversing the polarity of the current supplied to their stick circuits whereby such relays are released and placed in condition to be reenergized in accordance with a different code pattern.

LLOYD V. LEWIS. 

